Process for roll-to-roll manufacture of a display by synchronized photolithographic exposure on a substrate web

ABSTRACT

This invention relates to an electrophoretic display or a liquid crystal display and novel processes for its manufacture. The electrophoretic display (EPD) of the present invention comprises microcups of well-defined shape, size and aspect ratio and the microcups are filled with charged pigment particles dispersed in an optically contrasting dielectric solvent. The liquid crystal display (LCD) of this invention comprises well-defined microcups filled with at least a liquid crystal composition having its ordinary refractive index matched to that of the isotropic cup material. A novel roll-to-roll process and apparatus of the invention permits the display manufacture to be carried out continuously by a synchronized photo-lithographic process. The synchronized roll-to-roll process and apparatus permits a pre-patterned photomask, formed as a continuous loop, to be rolled in a synchronized motion in close parallel alignment to a web which has been pre-coated with a radiation sensitive material, so as to maintain image alignment during exposure to a radiation source. The radiation sensitive material may be a radiation curable material, in which the exposed and cured portions form the microcup structure. In an additional process step, the radiation sensitive material may be a positively working photoresist which temporarily seals the microcups. Exposure of a selected subset of the microcups via the photomask image permits selective re-opening, filling and sealing of the microcup subset. Repetition with additional colors permits the continuous assembly of a multicolor EPD or LCD display.

DESCRIPTION

[0001] This application is one of series of our co-pending applicationsby the same inventive entity pertaining to novel electrophoretic and LCDimage displays and subassemblies, and to novel methods of making suchdisplays and subassemblies. Certain of the inventions which aredisclosed in these related applications are also disclosed in thepresent application. The absence of claims in the present applicationdirected to any particular inventive subject matter disclosed herein isnot to be construed as intent by Applicants to forego patent protectionas to such subject matter.

FIELD

[0002] This invention relates to the field of electrophoretic displays,and more particularly to methods and processes for the manufacture ofsuch displays comprising cells of well-defined shape, size, and aspectratio, which cells are filled with charged pigment particles dispersedin a solvent. The processes disclosed include the roll-to-rollmanufacture of an electrophoretic display by synchronizedphotolithographic exposure on a substrate web.

BACKGROUND

[0003] The electrophoretic display is a non-emissive device based on theelectrophoresis phenomenon influencing charged pigment particlessuspended in a solvent. This general type of display was first proposedin 1969. An electrophoretic display typically comprises a pair ofopposed, spaced-apart plate-like electrodes, with spacers predetermininga certain distance between the electrodes. One of the electrodes istypically transparent. A suspension composed of a colored solvent andsuspended charged pigment particles is enclosed between the two plates.

[0004] When a voltage difference is imposed between the two electrodes,the pigment particles migrate to one side by attraction to the plate ofpolarity opposite that of the pigment particles. Thus the color showingat the transparent plate may be determined by selectively charging theplates to be either the color of the solvent or the color of the pigmentparticles. Reversal of plate polarity will cause the particles tomigrate back to the opposite plate, thereby reversing the color.Intermediate color density (or shades of grey) due to intermediatepigment density at the transparent plate may be obtained by controllingthe plate charge through a range of voltages.

[0005] Among the advantages of an electrophoretic display (EPD) overother types of flat panel displays is the very low power consumption.This salient advantage makes the EPD particularly suitable for portableand battery powered devices such as laptops, cell phones, personaldigital assistants, portable electronic medical and diagnostic devices,global positioning system devices, and the like.

[0006] In order to prevent undesired movements of the particles such assedimentation, partitions were proposed between the two electrodes fordividing the space into smaller cells. See, e.g., M. A Hopper and V.Novotny, IEEE Trans. Electr. Dev., Vol ED 26, No. 8, pp 1148-1152(1979). However, in the case of the partition-type electrophoreticdisplay, some difficulties are encountered in the formation of thepartitions and the process of enclosing the suspension. Furthermore, itis also difficult to keep different colors of suspensions separate fromeach other in the partition-type electrophoretic display.

[0007] Attempts have been made to enclose the suspension inmicrocapsules. U.S. Pat. No. 5,961,804 and U.S. Pat. No. 5,930,026describe microencapsulated electrophoretic displays. These displays havea substantially two dimensional arrangement of microcapsules each havingtherein an electrophoretic composition of a dielectric fluid and asuspension of charged pigment particles that visually contrast with thedielectric solvent. The microcapsules can be formed by interfacialpolymerization, in-situ polymerization or other known methods such asphysical processes, in-liquid curing or simple/complex coacervation. Themicrocapsules, after their formation, may be injected into a cellhousing two spaced-apart electrodes, or they may be “printed” into orcoated on a transparent conductor film. The microcapsules may also beimmobilized within a transparent matrix or binder that is itselfsandwiched between the two electrodes.

[0008] The electrophoretic displays prepared by these prior artprocesses, in particular the microencapsulation process, as disclosed inU.S. Pat. Nos. 5,930,026, 5,961,804, and 6,017,584, have severalshortcomings. For example, the electrophoretic displays manufactured bythe microencapsulation process suffer from sensitivity to environmentalchanges (in particular sensitivity to moisture and temperature) due tothe wall chemistry of the microcapsules. Secondly the electrophoreticdisplays based on the microcapsules have poor scratch resistance due tothe thin wall and large particle size of the microcapsules. To improvethe handleability of the display, microcapsules are embedded in a largequantity of polymer matrix which results in a slow response time due tothe large distance between the two electrodes and a low contrast ratiodue to the low payload of pigment particles. It is also difficult toincrease the surface charge density on the pigment particles becausecharge-controlling agents tend to diffuse to the water/oil interfaceduring the microencapsulation process. The low charge density or zetapotential of the pigment particles in the microcapsules also results ina slow response rate. Furthermore, because of the large particle sizeand broad size distribution of the microcapsules, the prior artelectrophoretic display of this type has poor resolution andaddressability for color applications.

SUMMARY

[0009] The electrophoretic display (EPD) of the present inventioncomprises cells of well-defined shape, size and aspect ratio and thecells are filled with charged pigment particles dispersed in anoptically contrasting dielectric solvent.

[0010] The invention also relates to a novel roll-to-roll process andapparatus which permit the manufacture of the display to be carried outcontinuously by a synchronized photo-lithographic process. Thesynchronized roll-to-roll process and apparatus are also useful formanufacturing liquid crystal displays (LCD) and other structures andassemblies for electronic devices.

[0011] One embodiment of the invention relates to the manufacture of aplurality of microcups which are formed integrally with one another asportions of a structured two-dimensional array assembly, preferablybeing formed upon a support web including a patterned conductor film,such as addressable indium-tin oxide (ITO) lines. Each microcup of thearray assembly is filled with a suspension or dispersion of chargedpigment particles in a dielectric solvent, and sealed to form anelectrophoretic cell.

[0012] The substrate web upon which the microcups are formed preferablyincludes a display addressing array comprising pre-formed conductorfilm, such as ITO conductor lines. The conductor film (ITO lines) andsupport web are coated with a radiation curable polymer precursor layer.The film and precursor layer are then exposed imagewise (as definedbelow) to radiation to form the microcup wall structure. Followingexposure, the precursor material is removed from the unexposed areas,leaving the cured microcup walls bonded to the conductor film/supportweb. The imagewise exposure may be by UV or other forms of radiationthrough a photomask to produce an image or predetermined pattern ofexposure of the radiation curable material coated on the conductor film.Although it is generally not required, the mask may be positioned andaligned with respect to the conductor film, i.e., ITO lines, so that thetransparent mask portions align with the spaces between ITO lines, andthe opaque mask portions align with the ITO material (intended formicrocup cell floor areas).

[0013] Alternatively, the microcup array may be prepared by a processincluding embossing a thermoplastic or thermoset precursor layer coatedon a conductor film with a pre-patterned male mold, followed byreleasing the mold. The precursor layer may be hardened by radiation,cooling, solvent evaporation, or other means. This novel micro-embossingmethod is included in the subject of our co-pending application entitled“An Improved Electrophoretic Display and Novel Process for ItsManufacture”, filed Mar. 4, 2000.

[0014] Solvent-resistant, thermomechanically stable microcups having awide range of size, shape, and opening ratio can be prepared by eitherone of the aforesaid methods.

[0015] Another embodiment of the invention relates to the manufacture ofa monochrome electrophoretic display from a microcup assembly by fillingthe microcups with a single pigment suspension composition, sealing themicrocups, and finally laminating the sealed array of microcups with asecond conductor film pre-coated with an adhesive layer.

[0016] A further embodiment of the invention relates to the manufactureof a color electrophoretic display from a microcup assembly by a processof sequential selective opening and filling of predetermined microcupsubsets. The process includes laminating or coating the pre-formedmicrocups with a layer of positively-working photoresist, selectivelyopening a certain number of the microcups by imagewise exposing thepositive photoresist, followed by developing the resist, filling theopened cups with a colored electrophoretic fluid, and sealing the filledmicrocups by a sealing process. These steps may be repeated to createsealed microcups filled with electrophoretic fluids of different colors.Thus, the array may be filled with different colored compositions inpredetermined areas to form a color electrophoretic display. Variousknown pigments and dyes provide a wide range of color options for bothsolvent phase and suspended particles. Known fluid application andfilling mechanisms may be employed.

[0017] Yet a further embodiment of the invention relates to asynchronized roll-to-roll photolithographic exposure method andapparatus, which may be employed for a number of useful processes,including the process of making the microcup array and the process ofselectively filling the array of microcups to form a color displayassembly. The imagewise roll-to-roll photolithographic exposure ispreferably done through a moving photomask synchronized with a movingweb substrate, to permit imagewise exposure of the workpiece (e.g.,microcup array or color display) in a continuous and seamless manner.

[0018] The pre-patterned photomask may be an elongate strip formed as acontinuous loop. The photomask pattern corresponds in form to structuresof the microcup array or other subject device, such as the microcupwalls and top openings. The photomask permits an image of the microcuparray structure to be projected by radiation passing through thephotomask. This “imagewise” exposure selectively exposes the radiationsensitive material to form the imaged structures while leaving theintervening material unexposed. The photomask loop is supported andaligned by an alignment mechanism so that the photomask loop is adjacentto the web, and a portion of the photomask loop is in generally parallelorientation to the portion of web to be exposed.

[0019] The synchronized motion of the photomask and web includes movingthe portion of the photomask loop which is adjacent to the web inparallel to the web in the substantially same direction. In effect, thephotomask loop is “rolled” in a synchronized motion relative to the webin close parallel proximity to the exposed web portion, so as tomaintain image alignment during exposure. The relative motion of the weband photomask is controlled so that the microcup pattern of the maskremains aligned with the corresponding structures being “imaged” on theweb during exposure. In a continuous synchronized motion and exposureprocess, the web and mask are moved at the same speed in the samedirection during exposure in order to maintain this constant alignment.

[0020] Alternatively, a semi-continuous synchronized motion may beemployed, whereby the mask and web are moved by equal incrementaldistances prior to exposure, but remain fixed during exposure.

[0021] For the roll-to-roll process, the photomask may be synchronizedin motion with the support web using mechanisms such as coupling orfeedback circuitry or common drives to maintain the coordinated motion(i.e., to move at the same speed).

[0022] For preparation of the array of discretely patterned microcups,the roll-to-roll photolithographic exposure apparatus can accept theconductor film/substrate web coated with radiation-curable compositionas a continuous strip in a high speed process. Following exposure, theweb moves into a development area where the unexposed material isremoved to form the microcup wall structure. The microcups and ITO linesare preferably of selected size and coordinately aligned with thephotomask, so that each completed display cell (i.e., filled and sealedmicrocup) may be discretely addressed and controlled by the displayprocessor. The ITO lines may be pre-formed by either a wet or dryetching process on the substrate web.

[0023] For making color displays from the microcup array, thesynchronized roll-to-roll exposure photolithographic process of theinvention permits the selective opening, filling and sealing ofpre-selected subsets of the microcup cells.

[0024] The pre-formed microcup array may be laminated or coated totemporarily seal the microcups with a positive-acting photoresistcomposition, and the sealed microcup array is then imagewise exposed(e.g., using a corresponding photomask) to selectively expose the topopenings of a desired subset of the microcups. Known laminating andcoating mechanisms may be employed. The exposed portion of thephotoresist may then be removed by developer to open the tops of theselected microcup subset. The term “developer” in this context refers tosuitable known means for selectively removing the exposed photoresist,while leaving the unexposed photoresist in place.

[0025] Thus, the array may be sequentially filled with several differentcolor compositions (typically three primary colors) in a pre-determinedcell pattern. For example, the imagewise exposure process may employ apositively working photoresist top laminate which initially seals theempty microcups. The microcups are then exposed through a mask (e.g., aloop photomask in the described roll-to-roll process) so that only afirst selected subset of microcups are exposed. Development with adeveloper removes the exposed photoresist and thus opens the firstmicrocup subset to permit filling with a selected color pigmentdispersion composition, and subsequent sealing by one of the methodsdescribed herein. The exposure and development process is repeated toexpose and open a second selected microcup subset for filling with asecond pigment dispersion composition, with subsequent sealing. Finally,the remaining photoresist is removed and the third subset of microcupsis filled and sealed.

[0026] Yet another embodiment of the invention relates to the sealing ofthe microcups after they are filled with the electrophoretic fluidcontaining a dispersion of charged pigment particles in a dielectricfluid. Preferably, the sealing is accomplished by dispersing athermoplastic or thermoset precursor in the electrophoretic fluid beforethe filling step. The thermoplastic or thermoset precursor is immisciblewith the dielectric solvent and has a specific gravity lower than thatof the solvent and the pigment particles. After filling, thethermoplastic or thermoset precursor phase separates from theelectrophoretic fluid and forms a supernatant layer at the top of thefluid.

[0027] The sealing of the microcups is then conveniently accomplished byhardening the precursor layer by solvent evaporation, interfacialreaction, moisture, heat, or radiation. UV radiation is the preferredmethod to seal the microcups, although a combination of two or morecuring mechanisms as described above may be used to increase thethroughput of sealing. Alternatively, the sealing can be accomplished byovercoating the electrophoretic fluid with a solution containing thethermoplastic or thermoset precursor. To reduce or eliminate the degreeof intermixing during the overcoating process, it is highly advantageousto use a sealing composition that is immiscible with the electrophoreticfluid and preferably has a specific gravity lower than the dielectricfluid. The sealing is then accomplished by hardening the precursor bysolvent evaporation, interfacial reaction, moisture, heat, radiation, ora combination of curing mechanisms. These sealing processes areespecially unique features of the present invention.

[0028] Liquid crystal displays may also be prepared by the method ofthis invention if the electrophoretic fluid described above is replacedby a suitable liquid crystal composition having the ordinary refractiveindex matched to that of the isotropic cup material. In the “on” state,the liquid crystal in the microcups is aligned to the field directionand is transparent. In the “off” state, the liquid crystal is notaligned and scatters light. To maximize the light scattering effect, thediameter of the microcups is typically in the range of 0.5-10 microns.

[0029] In summary, the roll-to-roll process of the present invention maybe employed to carry out a sequence of processes on a single continuousweb, by carrying and guiding the web to a plurality of process stationsin sequence.

[0030] For example, the microcups may be formed, filled, sealed andlaminated in a continuous sequence.

[0031] In addition to the formation and filling of microcup arrays, thesynchronized roll-to-roll process may be adapted to the preparation of awide range of structures or discrete patterns for electronic devicesformable upon a support web substrate, e.g., flexible circuit boards andthe like. As in the process and apparatus for EPD microcups describedherein, a pre-patterned photomask is prepared which includes a pluralityof photomask portions corresponding to structural elements of thesubject device. Each such photomask portion may have a pre-selectedtransparency to radiation or a pre-selected opacity to radiation, so asto form an image of such structural elements upon the correspondinglyaligned portion of the web during exposure. The methodology of theinvention may be used for selective curing of structural material, ormay be used to expose positively or negatively acting photoresistmaterial during manufacturing processes.

[0032] Because these multiple-step processes as disclosed may be carriedout roll-to-roll continuously or semi-continuously, they are suitablefor high volume and low cost production. These processes are alsoefficient and inexpensive as compared to other processes for high volumeproduction operations. The electrophoretic display prepared according tothe present invention is not sensitive to environment, such as humidityand temperature. The display is thin, flexible, durable, easy-to-handle,and format-flexible. Since the electrophoretic display preparedaccording to the present invention comprises cells of favorable aspectratio and well-defined shape and size, the bi-stable reflective displayhas excellent color addressability, high contrast ratio, and fastswitching rate. Furthermore, the disclosed apparatus and methods of theinvention are directed to electrophoretic displays (EPDs) suitable foreconomical mass production, thereby making the low power consumptioncharacteristics of the EPD available to a broader range of consumer,scientific, commercial and industrial electronics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a schematic cross-section depiction of theelectrophoretic display of the present invention, showing three microcupcells in a neutral condition.

[0034]FIG. 2 is a schematic cross-section depiction of theelectrophoretic display of FIG. 1, but with two of the cells charged, tocause the pigment to migrate to one plate.

[0035] FIGS. 3A-3C shows the contours of an exemplary microcup arrayprepared by the method of the invention, FIG. 3A showing a perspectiveview, FIG. 3B showing a plan view, and FIG. 3C showing an elevationview, the vertical scale being exaggerated for clarity.

[0036] FIGS. 4A-4D are a sequence of cross sections of an exemplarymicrocup array of the invention, illustrating the steps of a preferredmethod of assembly of the EPD of the invention, in this example, amonochrome display.

[0037]FIGS. 5A and 5B show the basic processing steps for preparing themicrocups involving imagewise photolithographic exposure through aphotomask (“top exposure”) of the conductor film coated with a thermosetprecursor to UV radiation.

[0038]FIGS. 6A and 6B show alternative processing steps for preparingthe microcups involving imagewise photolithographic exposure of the baseconductor film coated with a thermoset precursor to UV radiation, inwhich the base conductor pattern on a transparent substrate serves asubstitute for a photomask (“bottom exposure”) and is opaque to theradiation.

[0039]FIGS. 7A and 7B show alternative processing steps for preparingthe microcups involving imagewise photolithographic combining the topexposure and bottom exposure principles, whereby the walls are cured inone lateral direction by top photomask exposure and in the perpendicularlateral direction by bottom exposure through the opaque base conductorfilm (“combined exposure”).

[0040]FIGS. 8, 8A and 8B show the method steps of FIGS. 5A-C carried outby a novel synchronized roll-to-roll photo-lithographic apparatus of theinvention.

[0041]FIGS. 9A to 9H show an example of the preparation of a multi-colorelectrophoretic display by the method of the invention.

[0042]FIGS. 10, 10A and 10B show the method steps of FIGS. 9A-H carriedout by the novel synchronized roll-to-roll photo-lithographic apparatusof the invention using a positive acting photoresist laminate orcoating.

[0043]FIG. 11 illustrates schematically an exemplary semi-continuousprocess for the preparation of a 3-color EPD microcup array assembly.

DETAILED DESCRIPTION OF THE INVENTION

[0044] The following detailed description illustrates the invention byway of example, not by way of limitation of the principles of theinvention. This description will enable one skilled in the art to makeand use the invention, and describes several embodiments, adaptations,variations, alternatives and uses of the invention, including what ispresently believed to be the best mode of carrying out the invention.

[0045] In this regard, the invention is illustrated in several figures,and is of sufficient complexity that the many parts, interrelationships,and sub-combinations thereof simply cannot be clearly or meaningfullyillustrated in a single patent-type drawing. Accordingly, several of thedrawings show in schematic, or omit parts that are not essential in thatdrawing to a description of a particular feature, aspect or principle ofthe invention being disclosed. Thus, the best mode embodiment of onefeature may be shown in one drawing, and the best mode of anotherfeature will be shown in another drawing.

[0046] Certain examples are given herein to enable those skilled in theart to more clearly understand and to practice the present invention.These exemplary processes, methods, compositions and apparatus shouldnot be considered as limiting the scope of the invention, but merely asbeing illustrative and representative thereof.

[0047] All publications and patent applications cited in thisspecification are herein incorporated by reference as if each individualpublication or patent application were specifically and individuallyindicated to be incorporated by reference.

[0048] Definitions.

[0049] Unless defined otherwise in this specification, all technicalterms are used herein according to their conventional definitions asthey are commonly used and understood by those of ordinary skill in theart.

[0050] The term “microcup” refers to the cup-like indentations, whichmay be created by methods such as micro-embossing or imagewise exposure.Likewise, the plural form “microcups” in a collective context may ingeneral refer to the microcup assembly comprising a plurality of suchmicrocups integrally formed or joined to make a structuredtwo-dimensional microcup array.

[0051] The term “cell”, in the context of the present invention, isintended to mean the single unit formed from a sealed microcup. Thecells are filled with charged pigment particles dispersed in a solventor solvent mixture.

[0052] The term “well-defined”, when describing the microcups or cells,is intended to indicate that the microcup or cell has a definite shape,size and aspect ratio which are pre-determined according to the specificparameters of the manufacturing process.

[0053] The term “aspect ratio” is a commonly known term in the art ofelectrophoretic displays. In this application, the term “aspect ratio”as applied to the microcup refers to the depth to width ratio or thedepth to diameter of the microcup opening.

[0054] The term “imagewise exposure” means exposure of radiation-curablematerial or photoresist composition to radiation, such as UV, using oneof the methods of the invention, whereby the portions of the material soexposed are controlled to form a pattern or “image” corresponding to thestructure of the microcups, e.g., the exposure is restricted to theportions of the material corresponding to the microcup walls, leavingthe microcup floor portion unexposed. In the case of selectively openingphotoresist on predetermined portions of the microcup array, imagewiseexposure means exposure on the portions of material corresponding to thecup opening, leaving the microcup walls unexposed. The pattern or imagemay be formed by such methods as exposure through a photomask, oralternatively by controlled particle beam exposure, and the like.

[0055] Microcup Array And Methods Of The Invention.

[0056]FIGS. 1 and 2 are schematic cross-section views of an exemplarymicrocup array assembly embodiment, simplified for clarity, showing amicrocup array assembly (10) of three microcup cells (12 a, b, and e).

[0057] As shown in FIG. 1, each cell (12) of array (10) comprises twoelectrode plates (11, 13), at least one of which is transparent (11),such as an indium-tin oxide (ITO) electrode, the electrodes (11) and(13) bounding two opposite faces of the cell (12).

[0058] The microcup cell array assembly (10) comprises a plurality ofcells which are: disposed adjacent to one another within a plane to forma layer of cells (12) enclosed between the two electrodes layers (11)and (13). Three exemplary cells (12 a), (12 b), and (12 c) are shown,bounded by their respective electrode plates (11 a, 11 b, and 11 c)(transparent) and (13 a, 13 b, and 13 c) (back plates), it beingunderstood that a large number of such cells are preferably arrayedtwo-dimensionally (to the right/left and in/out of the plane in FIG. 1)to form a sheet-like display of any selected area and two-dimensionalshape. Likewise, several microcup cells may be bounded by a singleelectrode plate (11) or (13), although, for clarity, FIG. 1 shows anexample in which each cell (12) is bounded by separate electrode plates(11 and 13) having the width of a single cell.

[0059] The cells are of well-defined shape and size and are filled witha colored dielectric solvent (14) in which charged pigment particles(15) are suspended and dispersed. The cells (12) may be each filled withthe same composition of pigment and solvent (e.g., in a monochromedisplay) or may be filled with different compositions of pigment andsolvent (e.g., in a full color display). FIG. 1 shows three differentcolor combinations as indicated by the different hatch pattern in eachcell (12 a, 12 b, and 12 c), the solvents being designated (14 a, 14 b,and 14 c) respectively, and the pigment particles being designated (15a, 15 b, and 15 e) respectively.

[0060] The microcup cells (12) each comprise enclosing walls (16)bounding the cells on the sides (within the plane of array (10) andfloor (17) bounding the cell on one face, in this example the faceadjacent to electrode (13). On the opposite face (adjacent electrode(11)) each cell comprises sealing cap portion (18). Where the sealingcap portion is adjacent to the transparent electrode (11) (as in FIG.1), the sealing cap (18) comprises a transparent composition. Althoughin the example of FIG. 1, the floor (17) and the sealing cap (18) areshown as separate cell portions distinct from adjacent electrodes (13)and (11) respectively, alternative embodiments of the microcup array(10) of the invention may comprise an integral floor/electrode structureor an integral sealing cap/electrode structure.

[0061]FIG. 2 is a schematic cross-section depiction of theelectrophoretic display of FIG. 1, but with two of the cells charged (12a and 12 c), to cause the pigment to migrate to one plate. When avoltage difference is imposed between the two electrodes (11, 13), thecharged particles (15) migrate to one side (i.e., toward electrode (11or 13) depending on the charge of the particle and electrode), such thateither the color of the pigment particle (15) or the color of thesolvent (14) is seen through the transparent conductor film (11). Atleast one of the two conductors (11) or (13) is patterned (separatelyaddressable portions) to permit a selective electric field to beestablished with respect to either each cell or with respect to apre-defined group of cells (e.g., to form a pixel).

[0062] In the example of FIG. 2, two of the cells are shown charged (12a and 12 c), in which the pigment (15 a and 15 e) has migrated to therespective transparent electrode plates (11 a and 11 c). The remainingcell (12 b) remains neutral (pigment (15 b) is dispersed throughoutsolvent (14 b)).

[0063] FIGS. 3A-3C shows the contours of an exemplary portion of amicrocup array prepared by the method of the invention, FIG. 3A showinga perspective view, FIG. 3B showing a plan view, and FIG. 3C showing anelevation view, the vertical scale being exaggerated for clarity. Forreflective electrophoretic displays, the opening area of each individualmicrocup may preferably be in the range of about 10² to about 5×10⁵ μm²,more preferably from about 10³ to about 5×10⁴ μm². The width w of themicrocup (12) (distance between adjacent walls (16)) may vary over awide range, and is selectable to suit the desired final displaycharacteristics. The width w of the microcup openings preferably is inthe range of from about 15 to about 450 μm, and more preferably fromabout 25 to about 300 μm from edge to edge of the openings. Eachmicrocup may form a small segment of a pixel of the final display, ormay be a full pixel.

[0064] The wall thickness t relative to the cup width w may vary over alarge range, and is selectable to suit the desired final displaycharacteristics. The microcup wall thickness is typically from about0.01 to about 1 times the microcup width, and more preferably about 0.05to about 0.25 times the microcup width. The opening-to-wall area ratiois preferably in the range of from about 0.05 to about 100, morepreferably from about 0.4 to about 20.

[0065] The microcup wall height h (which defines the cup depth) is shownexaggerated beyond its typical proportional dimensions for clarity.Although the wall height may be of a wide range relative to the cupwidth w, the optimum height will depend to an extent on the solvent andpigment characteristics and the desired operating electric field. Thusthe wall height may be selected to optimize the display responsecharacteristics, and need not be any fixed relationship to cell width.The proportional height of the wall may typically be greater incomparison to a small micro cup width than in comparison to a largemicrocup width. Most typically, the wall height is less than themicrocup width. Preferably, the height of the microcups is in the rangeof about 3 to about 100 microns (μm), preferably from about 10 to about50 μm.

[0066] For simplicity and clarity, a square microcup arranged in alinear two-dimensional array assembly is assumed in the descriptionherein of the microcup array assembly of the invention. However, themicrocup need not be square, it may be rectangular, circular, or a morecomplex shape if desired. For example, the microcups may be hexagonaland arranged in a hexagonal close-packed array, or alternatively,triangular cups may be oriented to form hexagonal sub-arrays, which inturn are arranged in a hexagonal close-packed array.

[0067] In general, the microcups can be of any shape, and their sizesand shapes may vary throughout the display. This may be advantageous inthe color EPD. In order to maximize the optical effect, microcups havinga mixture of different shapes and sizes may be produced. For example,microcups filled with a dispersion of the red color may have a differentshape or size from the green microcups or the blue microcups.Furthermore, a pixel may consist of different numbers of microcups ofdifferent colors. For example, a pixel may consist of a number of smallgreen microcups, a number of large red microcups, and a number of smallblue microcups. It is not necessary to have the same shape and numberfor the three colors.

[0068] The openings of the microcups may be round, square, rectangular,hexagonal, or any other shapes. The partition area between the openingsis preferably kept small in order to achieve a high color saturation andcontrast while maintaining desirable mechanical properties. Consequentlythe honeycomb-shaped opening is preferred over, for example, thecircular opening.

[0069] Preparation Of Electrophoretic Displays from the Microcup Array.

[0070] The preferred process of preparing the microcup array isillustrated schematically in FIGS. 4A-4D.

[0071] As shown in FIG. 4A, the microcup array (40) may be prepared byany of the alternative methods of the invention, such as those examplesillustrated in FIGS. 5, 6 and 7. The unfilled microcup array made by themethods described herein typically comprises a substrate web (43) uponwhich a base electrode (42) is deposited. The microcup walls (41) extendupward from the substrate (43) to form the open cups.

[0072] As shown in FIG. 4B, the microcups are filled with a suspensionof the charged pigment particles (45) in a colored dielectric solventcomposition (44). In the example shown, the composition is the same ineach cup, i.e., in a monochrome display. An example of the assembly of acolor display, in which three different colored solvent/pigmentcompositions are employed, is described below in FIG. 9.

[0073] As shown in FIG. 4C, after filling, the microcups are sealed witha sealing or cap layer (46), which bonds to the microcup walls andprevents solvent leakage. In one currently preferred sealing method, athermoset precursor sealing composition (46 a) is added to thesolvent/pigment composition (44/45). The thermoset precursor (46 a)composition preferably is not miscible or soluble in the solvent and hasa lower specific gravity than the solvent and the pigment particles. Thethermoset precursor (46 a) separates and forms a supernatant layer ontop of the liquid phase solvent (44). The thermoset precursor (46 a)preferably is then cured by radiation such as UV (alternatively by heator moisture) to form a bonded seal cap (46 b) enclosing the microcups(40). Alternatively, the sealing of the microcups may be accomplished bydirectly overcoating and curing a layer of the thermoset precursorcomposition over the surface of the electrophoretic fluid. More detailsof the sealing methods are discussed in the following sections.

[0074] As shown in FIG. 4D, the sealed array of electrophoretic microcupcells (40) is laminated With a second conductor film (47), preferably bypre-coating the conductor (47) with an adhesive layer (48) which may bea pressure sensitive adhesive, a hot melt adhesive, or a heat, moisture,or radiation curable adhesive. The laminate adhesive may be post-curedby radiation such as UV through the top conductor film if the latter istransparent to the radiation.

[0075] Preparation of the Pigment/Solvent Suspension or DispersionComposition

[0076] As described herein with respect to the various embodiments ofthe EPD of the invention, the microcups are preferably filled withcharged pigment particles dispersed in a dielectric solvent (e.g.,solvent (44) and pigment particles (45) in FIG. 4B.). The dispersion maybe prepared according to methods well known in the art, such as U.S.Pat. Nos. 6,017,584, 5,914,806, 5,573,711, 5,403,518, 5,380,362,4,680,103, 4,285,801, 4,093,534, 4,071,430, and 3,668,106. See also IEEETrans. Electron Devices, ED-24, 827 (1977), and J. Appl. Phys. 49(9),4820 (1978).

[0077] The charged pigment particles visually contrast with the mediumin which the particles are suspended. The medium is a dielectric solventwhich preferably has a low viscosity and a dielectric constant in therange of about 2 to about 30, preferably about 2 to about 15 for highparticle mobility. Examples of suitable dielectric solvents includehydrocarbons such as decahydronaphthalene (DECALIN),5-ethylidene-2-norbornene, fatty oils, paraffin oil, aromatichydrocarbons such as toluene, xylene, phenylxylylethane, dodecylbenzeneand alkylnaphthalene, halogenated solvents such asdichlorobenzotrifluoride, 3,4,5-trichlorobenzotriflouride,chloropentafluoro-benzene, dichlorononane, pentachlorobenzene, andperfluoro solvents such as perfluorodecalin, perfluorotoluene,perfluoroxylene, FC-43, FC-70 and FC-5060 from 3M Company, St. PaulMinn., low molecular weight halogen containing polymers such aspoly(perfluoropropylene oxide) from TCI America, Portland, Oreg.,poly(chlorotrifluoroethylene) such as Halocarbon Oils from HalocarbonProduct Corp., River Edge, N.J., perfluoropolyalkylether such as Galden,HT-200, and Fluorolink from Ausimont or Krytox Oils and Greases K-FluidSeries from DuPont, Delaware. In one preferred embodiment,poly(chlorotrifluoroethylene) is used as the dielectric solvent. Inanother preferred embodiment, poly(perfluoropropylene oxide) is used asthe dielectric solvent.

[0078] The non-migrating fluid colorant may be formed from dyes orpigments. Nonionic azo and anthraquinone dyes are particularly useful.Examples of useful dyes include, but are not limited to: Oil Red EGN,Sudan Red, Sudan Blue, Oil Blue, Macrolex Blue, Solvent Blue 35, PylamSpirit Black and Fast Spirit Black from Pylam Products Co., Arizona,Sudan Black B from Aldrich, Thermoplastic Black X-70 from BASF, andanthraquinone blue, anthraquinone yellow 114, anthraquinone red 111,135, anthraquinone green 28 from Aldrich. Fluorinated dyes areparticularly useful when perfluoro solvents are used. In the case of apigment, the non-migrating pigment particles for generating the color ofthe medium may also be dispersed in the dielectric medium. These colorparticles are preferably uncharged. If the non-migrating pigmentparticles for generating color in the medium are charged, theypreferably carry a charge which is opposite from that of the chargedmigrating pigment particles. If both types of pigment particles carrythe same charge, then they should have different charge density ordifferent electrophoretic mobility. In any case, the dye or pigment forgenerating the non-migrating fluid colorant of the medium must bechemically stable and compatible with other components in thesuspension.

[0079] The charged, migrating pigment particles may be organic orinorganic pigments, such as TiO₂, phthalocyanine blue, phthalocyaninegreen, diarylide yellow, diarylide AAOT Yellow, and quinacridone, azo,rhodamine, perylene pigment series from Sun Chemical, Hansa yellow Gparticles from Kanto Chemical, and Carbon Lampblack from Fisher.Submicron particle size is preferred. These particles should haveacceptable optical characteristics, should not be swollen or softened bythe dielectric solvent, and should be chemically stable. The resultingsuspension must also be stable against sedimentation, creaming orflocculation under normal operating conditions.

[0080] The migrating pigment particles may exhibit a native charge, ormay be charged explicitly using a charge control agent, or may acquire acharge when suspended in the dielectric solvent. Suitable charge controlagents are well known in the art; they may be polymeric or non-polymericin nature, and may also be ionic or non-ionic, including ionicsurfactants such as Aerosol OT, sodium dodecylbenzenesulfonate, metalsoaps, polybutene succinimide, maleic anhydride copolymers,vinylpyridine copolymers, vinylpyrrolidone copolymer (such as Ganex fromInternational Specialty Products), (meth)acrylic acid copolymers,N,N-dimethylaminoethyl (meth)acrylate copolymers. Fluorosurfactants areparticularly useful as charge controlling agents in perfluorocarbonsolvents. These include FC fluorosurfactants such as FC-170C, FC-171,FC-176, FC430, FC431 and FC-740 from 3M Company and Zonylfluorosurfactants such as Zonyl FSA, F SE, FSN, FSN-100, FSO, FSO-100,FSD and UR from Dupont.

[0081] Suitable charged pigment dispersions may be manufactured by anyof the well-known methods including grinding, milling, attriting,microfluidizing, and ultrasonic techniques. For example, pigmentparticles in the form of a fine powder are added to the suspendingsolvent and the resulting mixture is ball milled or attrited forseveral: hours to break up the highly agglomerated dry pigment powderinto primary particles. Although less preferred, a dye or pigment forproducing the non-migrating fluid colorant may be added to thesuspension during the ball milling process.

[0082] Sedimentation or creaming of the pigment particles may beeliminated by microencapsulating the particles with suitable polymers tomatch the specific gravity to that of the dielectric solvent.Microencapsulation of the pigment particles may be accomplishedchemically or physically. Typical microencapsulation processes includeinterfacial polymerization, in-situ polymerization, phase separation,coacervation, electrostatic coating, spray drying, fluidized bed coatingand solvent evaporation.

[0083] For a black/white electrophoretic display, the suspensioncomprises charged white particles of titanium oxide (TiO₂) dispersed ina black solvent or charged black particles dispersed in a dielectricsolvent. A black dye or dye mixture such as Pylam Spirit Black and FastSpirit Black from Pylam Products Co. Arizona, Sudan Black B fromAldrich, Thermoplastic Black X-70 from BASF, or an insoluble blackpigment such as carbon black may be used to generate the black color ofthe solvent. For other colored suspensions, there are manypossibilities. For a subtractive color system, the charged TiO₂particles may be suspended in a dielectric solvent of cyan, yellow ormagenta color. The cyan, yellow or magenta color may be generated viathe use of a dye or a pigment. For an additive color system, the chargedTiO₂ particles may be suspended in a dielectric solvent of red, green orblue color generated also via the use of a dye or a pigment. The red,green, blue color system is preferred for most applications.

EXAMPLE 1 Pigment Dispersion.

[0084] Polystyrene (0.89 grams, Polysciences Inc., mw. 50,000) and AOT(0.094 grams, American Cyanamide, sodium dioctylsulfosuccinate) weredissolved in 17.77 grams of hot xylene (Aldrich). Ti-Pure R-706 (6.25grams) was added to the solution and ground in an attritor at 200 rpmfor more than 12 hours. A low viscosity, stable dispersion was obtained.Oil-blue N (0.25 grams, Aldrich) was added to color the dispersion. Thesuspension was then tested in a standard electrophoretic cell comprisingtwo ITO conductor plates separated by a 24 micron spacer. High contrast,alternating white and blue images were observed with a switching rate ofabout 60 Hz and a rising time of 8.5 msec at 80 volts.

EXAMPLE 2 Pigment Dispersion.

[0085] The test of Pigment Dispersion Example 1 was repeated, except OilRed EGN (Aldrich) was used. High contrast, alternating red and whiteimages were observed with a switching rate of 60 Hz and a rising time of12 msec at 60 volts.

EXAMPLE 3 Pigment Dispersion.

[0086] Ti-Pure R-706 (112 grams) was ground by an attritor in a solutioncontaining 11.2 grams of a maleic anhydride copolymer (Baker HughesX-5231), 24 grams of 3,4-dichlorobenzotrifluoride, and 24 grams of1,6-dichlorohexane (both from Aldrich). Similarly, 12 grams of carbonblack were ground in a solution containing 1.2 grams of alkylatedpolyvinylpyrrolidone (Ganex V216 from ISP), 34 grams of3,4-dichlorobenzotrifluoride, and 34 grams of 1,6-dichlorohexane(Aldrich) at 100° C. These two dispersions were then mixed homogeneouslyand tested. High contrast black and white images were observed with aswitching rate up to 10 Hz and a rising time of about 36 msec at 100volts.

EXAMPLE 4 Pigment Dispersion.

[0087] 6.42 Grams of Ti Pure R706 was dispersed with a homogenizer intoa solution containing 1.94 grams of Fluorolink D from Ausimont, 0.22grams of Fluorolink 7004 also from Ausimont, 0.37 grams of a fluorinatedcyan dye from 3M, and 52.54 grams of perfluoro solvent HT-200(Ausimont).

EXAMPLE 5 Pigment Dispersion.

[0088] The same as Example 4, except the Ti Pure R706 and Fluorolinkwere replaced by polymer coated TiO₂ particles from Elimentis (Hihstown,N.J.) and Krytox (from Du Pont) respectively.

[0089] Sealing of the Microcup Array.

[0090] The filled microcups of the array are enclosed and sealed, e.g.,as shown in FIG. 4C. The sealing of the microcups may be accomplished ina number of ways. As discussed earlier, a preferred approach is todisperse a UV curable composition containing multifunctional acrylates,acrylated oligomers, and photoinitiators into an electrophoretic fluidcontaining charged pigment particles dispersed in a colored dielectricsolvent. The UV curable composition is immiscible with the dielectricsolvent and has a specific gravity lower than that of the dielectricsolvent and the pigment particles. The two components, UV curablecomposition and: the electrophoretic fluid, are thoroughly blended in anin-line mixer and immediately coated onto the microcups with a precisioncoating mechanism such as Myrad bar, gravure, doctor blade, slot coatingor slit coating. Excess fluid is scraped away by a wiper blade or asimilar device. A small amount of a weak solvent or solvent mixture suchas isopropanol, methanol, or their aqueous solutions may be used toremove the residual electrophoretic fluid on the top surface of thepartition walls of the microcups. Volatile organic solvents may be usedto control the viscosity and coverage of the electrophoretic fluid. Thethus-filled microcups are then dried and the UV curable sealingcomposition floats to the top of the electrophoretic fluid. Themicrocups may be sealed by curing the supernatant UV curable layerduring or after it floats to the top. UV or other forms of radiationsuch as visible light, IR and electron beam may be used to cure and sealthe microcups. Alternatively, heat or moisture may also be employed tocure and seal the microcups, when heat or moisture curable compositionsare used.

[0091] A preferred group of dielectric solvents exhibiting desirabledensity and solubility discrimination against acrylate monomers andoligomers are halogenated hydrocarbons and their derivatives.Surfactants may be used to improve the adhesion and wetting at theinterface between the electrophoretic fluid and the sealing materials.Useful surfactants include the FC surfactants from 3M Company, Zonylfluorosurfactants from DuPont, fluoroacrylates, fluoromethacrylates,fluoro-substituted long chain alcohols, perfluoro-substituted long chaincarboxylic acids and their derivatives.

[0092] Alternatively, the electrophoretic fluid and the sealingprecursor may be coated sequentially into the microcups, if the sealingprecursor is at least partially compatible with the dielectric solvent.Thus, the sealing of the microcups may be accomplished by overcoating athin layer of thermoset precursor which is curable by radiation, heat,moisture or interfacial reactions and curing on the surface of thefilled microcups. Interfacial polymerization followed by UV curing isvery beneficial to the sealing process. Intermixing between theelectrophoretic layer and the overcoat is significantly suppressed bythe formation of a thin barrier layer at the interface by interfacialpolymerization. The sealing is then completed by a post curing step,preferably by UV radiation. To further reduce the degree of intermixing,it is highly desirable that the specific gravity of the overcoating issignificantly lower than that of the electrophoretic fluid. Volatileorganic solvents may be used to adjust the viscosity and the thicknessof the coatings. When a volatile solvent is used in the overcoat, it ispreferred that it is immiscible with the dielectric solvent. Thetwo-step overcoating process is particularly useful when the dye used isat least partially soluble in the thermoset precursor.

EXAMPLE 6 Microcup Sealing.

[0093] In this example of the “one-step” process of the invention,approximately 0.05 Milliliter of UV curable composition comprising 1 wt% of benzil dimethyl ketal (Esacure KB1 from Sartomer) in HDDA(1,6-hexanediol diacrylate from Aldrich) were dispersed into 0.4 ml of adielectric solvent comprising 0.5 wt % of 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-nonadecafluoro-1-decanol (Aldrich) in FC-43from 3M Company. The resultant dispersion was then immediately filledinto an array of microcups. Excess of fluid was scrapped away by a wiperblade. The HDDA solution was allowed to phase separate for at least 30seconds and cured by UV radiation (10 mw/cm²) for about 1 minute. Ahard, clear layer was observed on the top of the microcups and themicrocups were sealed.

EXAMPLE 7 Microcup Sealing.

[0094] In this example, the two-step overcoating and UV curing processof the invention was tested. The electrophoretic dispersion fluid, asprepared in Pigment Dispersion Example 3, was coated onto the microcuparray. A thin layer of Norland optical adhesive NOA 60 (Norland ProductsInc., New Brunswick, N.J.) was coated onto the filled microcups. Anyexcess of the UV adhesive was scrapped off by a strip of Mylar film andcleaned by a piece of absorbing paper. The overcoated adhesive was thencured immediately under a Loctite Zeta 7410 UV exposure unit for about15 minutes. The microcups were sealed completely and no air pocket wasobserved. The thickness of cured adhesive layer was about 5-10 micronsas measured by a Mitutoyo thickness gauge.

EXAMPLE 8 Microcup Sealing.

[0095] In this example, the two-step overcoating and moisture curingprocess of the invention was tested. The test of Microcup SealingExample 2 was repeated, except the Norland adhesive was replaced byInstant Krazy Glue from Elmer's Products, Inc., Columbus, Ohio. Theovercoated adhesive was then cured for 5 minutes by moisture in air. Themicrocups were sealed completely and no air pocket was observed. Thethickness of cured adhesive layer was about 5-10 microns as measured bya Mitutoyo thickness gauge.

EXAMPLE 9 Microcup Sealing.

[0096] In this example, the two-step overcoating and interfacialpolymerization process of the invention was performed. The experiment ofMicrocup Sealing Example 3 was repeated, except the electrophoreticfluid was replaced by a 3,4-dichlorobenzotrifluoride solution containing0.3 wt % of tetraethylenepentaamine (Aldrich) and the Instant Krazy gluewas replaced by an aliphatic polyisocyanate (Desmodur N 3300 from BayerCorp.) solution in anhydrous ether. A highly crosslinked thin film wasobserved almost immediately after overcoating. The dielectric solventwas completely sealed inside the microcups after the ether wasevaporated at room temperature. No air pocket was observed.

EXAMPLE 10 Microcup Sealing.

[0097] The samples prepared by the Pigment Dispersion Examples 4 and 5in perfluoro solvent HT200 were diluted with a volatile perfluorocosolvent FC-33 from 3M and coated onto a microcup array. The volatilecosolvent was allowed to be evaporated to expose a partially filledmicrocup array. A 7.5% solution of polyisoprene in heptane was thenovercoated onto the partially filled cups by a Universal BladeApplicator with an opening of 6 mil. The overcoated microcups were thendried at room temperature. A seamless sealing layer of about 7 micronsthickness was observed under microscope. Little entrapped air bubble wasobserved in the sealed microcups. The sample was then post treated by UVradiation or thermal baking to further improve the barrier properties.

EXAMPLE 11 Preparation Of The Radiation-Curable Material.

[0098] The composition shown in Table 1 was coated onto Mylar J101/200gauge web using a Nickel Chrome bird type film applicator with anopening of 3 mil. The solvent was allowed to evaporate leaving behind atacky film with a Tg (glass transition temperature) below roomtemperature. The coated web was then exposed through a mask and UV curedby a UV source such as a metal fluoride lamp. TABLE 1 PMMA-containing UVcurable composition No. Description Ingredient Supplier parts 1 Epoxyacrylate Ebecryl 3605 UCB 7.35 Chemicals 2 Monomer Sartomer SR205Sartomer 9.59 3 Urethane acrylate Ebecryl 6700 UCB 4.87 Chemicals 4Polymethyl- Elvacite 2051 ICI 9.11 methacrylate 5 Photoinitiator Darocur1173 Ciba 1.45 6 Cationic photoinitiator Cyracure UVI 6976 Union 0.60Carbide 7 Solvent Acetone Aldrich 67.03 Total 100.00

[0099] The solvents for removing the uncured composition following theimagewise exposure of the method of the invention may be conventional.The solvents may be conventional solvents or solvent mixtures which areselected to minimize the degree of swelling of the image-curedcomposition. Typical solvents include MEK, MPK, EtOAc, BuOH,isopropanol, methanol, cyclohexanone, dichloroethane, trichloroethane,methoxyethyl alcohol, and the like.

EXAMPLE 12 Preparation Of The Radiation-Curable Cup Material.

[0100] 12 Parts of Ebercryl 600 (UCB Chemicals, Smyrna, Ga.), 2.7 partsof Ebecryl 4827, 1 part of Ebecryl 1360, 6 parts of HDDA (UCBChemicals), and 1 part of Irgacure 500 (Ciba Specialty Chemicals,Tarrytown, N.Y.), were mixed homogeneously with 5 parts of methyl ethylketone (MEK). The solution was coated onto an ITO/PET film by Myrad barwith a target dry thickness of 50 microns. The coated sample was thenexposed through a mask and developed with isopropanol.

EXAMPLE 13 Preparation Of The Radiation-Curable Cup Material.

[0101] The same as Example 12, except the formulation was replaced by 12parts of Ebecryl 830, 5.5 parts of SR399 (Sartomer, Exton, Pa.), 2 partsof HDDA, 0.488 parts of Ebecryl 1360, 0.1 v parts of Irgacure 369 (CibaSpecialty Chemicals), 0.02 parts of isopropyl thioxanthone (ITX) fromAldrich, and 10 parts of MEK.

EXAMPLE 14 Preparation Of The Radiation-Curable Cup Material.

[0102] The same as Example 13, except the formulation was replaced by 7parts of Ebecryl 600, 8 parts of SR399, 1 part of HDDA, 2.6 parts ofEbecryl 4827, 1.4 parts of Ebecryl 1360, 0.1 parts of Irgacure 369, 0.02parts of ITX, and 10 parts of MEK.

[0103] Photolithographic Method of Preparation of the Microcup Assembly.

[0104] The general photolithographic process embodiments for preparationof the microcup assembly of the invention ((40) in FIG. 4) are shown inFIGS. 5, 6 and 7, and the description of the particular synchronizedroll-to-roll photo-lithographic apparatus and method of the invention isgiven below.

[0105] Top exposure method embodiment. As shown in FIGS. 5A and 5B, themicrocup array (50) may be prepared by exposure of a radiation curablematerial (51 a) coated by known methods onto a conductor electrode film(52) to UV light (or alternatively other forms of radiation, electronbeams and the like) through a mask (56) to form walls (51 b)corresponding to the image projected through the mask (56). The baseconductor film (52) is preferably mounted on a supportive substrate baseweb (53), which may comprise a plastic material.

[0106] In the photomask (56) in FIG. 5A, the dark squares (54) representthe opaque area and the space between the dark squares represents theopening (transparent) area (55) of the mask (56). The UV radiatesthrough the opening area (55) onto the radiation curable material (51a). The exposure is preferably directly onto the radiation curablematerial (51 a), i.e., the UV does not pass through the substrate (53)or base conductor (52) (top exposure). For this reason, neither thesubstrate (53) nor the conductor (52) needs to be transparent to the UVor other radiation wavelengths employed.

[0107] As shown in FIG. 5B, The exposed areas (51 b) become hardened andthe unexposed areas (51 c) (protected by the opaque area (54) of themask (56)) are then removed by an appropriate solvent or developer toform the microcups (57). The solvent or developer is selected from thosecommonly used for dissolving or reducing the viscosity of radiationcurable materials such as methylethylketone, toluene, acetone,isopropanol or the like. The preparation of the microcups may besimilarly accomplished by placing a photomask underneath the conductorfilm/substrate base web and in this case the UV light radiates throughthe photomask from the bottom.

[0108] Bottom Exposure And Combination Method. Two alternative methodsfor the preparation of the microcup array of the invention by imagewiseexposure are illustrated in FIGS. 6A and 6B and 7A and 7B. These methodsemploy UV exposure through the substrate web, using the conductorpattern as a mask.

[0109] In FIG. 6A, the conductor film (62) used is pre-patterned tocomprise cell base electrode portions (64) corresponding to the floorportions of the microcups (67). The base portions (64) are opaque to theUV wavelength (or other radiation) employed. The spaces (65) betweenconductor base portions (62) are substantially transparent ortransmissive to the UV light. In this case, the conductor pattern servesas a photomask. The radiation curable material (61 a) is coated upon thesubstrate (63) and the conductor film (62) as described in FIG. 6A. Thematerial (61 a) is exposed by UV light projected “upwards” (throughsubstrate (63) and cured where not shielded by the conductor (62), i.e.,in those areas corresponding to the space (65). As shown in FIG. 6B, theuncured material (61 c) is removed from the unexposed areas as describedabove, leaving the cured material (61 b) to form the walls of themicrocups (67).

[0110]FIG. 7A illustrates a combination method which uses both the topand bottom exposure principals to produce the microcup array (70) of theinvention. The base conductor film (72) is also opaque andline-patterned. The radiation curable material (71 a), which is coatedon the base conductor (72) and substrate (73), is exposed from thebottom through the conductor line pattern (72) which serves as the firstphotomask. A second exposure is performed from the “top” side throughthe second photomask (76) having a line pattern perpendicular to theconductor lines (72). The spaces (75) between the lines (74) aresubstantially transparent or tranmissive to the UV light. In thisprocess, the wall material (71 b) is cured from the bottom up in onelateral orientation, and cured from the top down in the perpendiculardirection, joining to form an integral microcup (77).

[0111] As shown in FIG. 7B, the unexposed area is then removed by asolvent or developer as described above to reveal the microcups (77).

[0112] Synchronized Roll-to-Roll Photo-lithographic Process For MakingMicrocups.

[0113] The photo-lithographic method of making microcup arrays disclosedherein (e.g., as described in FIGS. 5A and 5B) may also be employed asthe principle for a novel synchronized roll-to-roll photo-lithographicprocess. For the roll-to-roll process, the photomask may be synchronizedwith the substrate web and moved at the same speed as the latter, so asto permit a continuous production of the microcup array of the inventionin the form of a continuous strip assembly.

[0114] In the preferred exemplary roll-to-roll process disclosed herein,the electrodes are disposed in orthogonal electrode lines (“ITO lines”)which may be aligned with the microcups (i.e., the walls of the cups arealigned with the spaces between base ITO lines). Compartmentalization ofthe space by walls formed between the electrodes (the walls forming themicro-cup boundaries) facilitates pixelation and x-y addressing of theindividual pixel (microcup). For x-y addressing of individual cup andhence pixel, the electrode lines will be orthogonal (i.e., the topelectrode lines will be orthogonal to the base electrode lines). Themicro-cups are therefore preferably positioned to be at theintersections of the perpendicular top and base ITO lines, when themicrocup cell assembly process is complete (e.g., see FIG. 4). The baseelectrode or ITO lines is consequently deposited or embedded within thesubstrate web as a patterned series of parallel conductor lines prior tothe microcup construction. The ITO lines are preferably of the samewidth as the micro-cups.

[0115] Addressable EPDs are known, and various techniques have beenproposed to solve addressability problems, such as the threshold voltageproblem, including the control electrode technique. See, e.g., B. Singerand A. L. Dalisa, Proc. SID, Vol. 18/3&4, 3^(rd) and 4^(th) Quarters, pp255-266 (1977). It should be understood, however, that the synchronizedroll-to-roll photo-lithographic process is inherently flexible, and maybe employed to make EPD microcup arrays of a wide range of electrodeconfigurations and electronic designs. Alternatively, for example,electronic components and/or conductors of various types may be embeddedwithin the substrate web or overlain on either side of the web prior tosupplying the web for the roll-to-roll process described herein and thesubsequent formation of microcups upon the web. Likewise, suchcomponents may be applied or mounted to the underside of the webfollowing formation of the microcups. Similarly, the microcupconstruction processes described herein may be employed to make cup-likecompartments for displays and other devices in addition to EPD.

[0116]FIG. 8 illustrates an exemplary embodiment of the preferredroll-to-roll photo-lithographic production apparatus (80) of theinvention for making the microcup array (81) for the electrophoreticdisplay of the invention, and shows a cross-section through theapparatus (80) and a developing continuous strip microcup array (81).The microcup array may be prepared by imagewise exposing through aphotomask (82) of radiation curable materials (84 a) coated so as tocover the substrate web (86) and conductor film ITO lines (88). Knowncoating mechanisms may be used to apply the material (84 a) to the web(86).

[0117] The curable material (84 a) is preferably UV curable, and iscured by the UV radiation shown in FIG. 8 to form a stable, solidpolymeric material (84 b) where the UV passes through the mask (82) tobe absorbed by the precursor material (84 a).

[0118] The orientation of the device (80) in FIG. 8 is only exemplary,and the elements may be re-arranged in many suitable orientations withrespect to the vertical direction for carrying out the method stepsshown. Additional conventional supports, such as guides, rollers and thelike, may be used to support, tension, turn, and/or twist the web (86)and microcup array (81) during the process shown.

[0119] The synchronized roll-to-roll process of the invention, asembodied in apparatus (80), includes mounting both photomask (82) andsubstrate web (86) in a manner that both are continuously movable andaligned adjacent one another, so that UV projection through the mask(82) and consequent curing of material (84 a) may take place on acontinuous and seamless manner.

[0120] In the preferred mounting arrangement shown in FIG. 8, the mask(82) is formed as a continuous loop, and is mounted to engage in tensionat least a spaced-apart pair of drive/support cylinders (90) and (91),the mask loop (82) having a substantial straight section (92) spanningbetween the curved portions (93) which fit around the drive cylinders(90) and (91).

[0121] The continuous strip substrate web (86), upon which the microcuparray (81) is constructed, similarly engages and passes around at leasttwo spaced apart drive cylinders (100, 101), so that a straight portion(103) of the web (86) is aligned parallel to the straight section of themask loop (82). The mask drive cylinders (90, 91) are driven to rotatein the direction shown as Arrows A, and the web drive cylinders (100,101) are driven to rotate in the opposite direction shown as Arrows B,so as to cause the mask straight section (92) and web straight section(103) to move in parallel, in the same direction, at the same speed. Therespective mask and web straight sections (92) and (103) respectivelyare preferably disposed a selected small distance apart, so as toprevent contamination of the mask (82) from the undeveloped material (84a).

[0122] In FIG. 8, the continuous web (86) is shown being fed inward(towards the UV exposure section) from the right-hand side, beingsupplied from a web storage/tensioner device (104) (not shown).Similarly, the developed web (with formed microcups) is shown beingtaken up by a second web storage/tensioner device (105) (not shown) asit moves outward (away from the UV exposure section). Devices (104 and105) may comprise known web handling and drive mechanisms.

[0123] Alternatively to on-site coating of radiation curable materials(84 a) onto the substrate web (86) and conductor film ITO lines (88), asshown in FIG. 8, a pre-coated web/ITO stock may be separately preparedand stored, e.g., in a roll form. The stored pre-coated web/ITO stockpreferably is formulated to be dry and tack-free after drying, toimprove storability. For this alternative, a higher process temperaturemay be used for the UV exposure step, than is typically used for on-sitecoated web (which may be tacky in its uncured state). The pre-coatedstock may then be unrolled at point (104) and fed to drive cylinder(100).

[0124] Following UV exposure, the UV curable material (84 a) is washedor developed with a suitable solvent which removes the uncured(non-exposed) material (84 a) to leave the cured material (84 b) inplace, forming the walls of the microcups. The term “solvent” in thiscontext refers to a suitable known means for selectively developing thematerial by removing the unexposed precursor, while leaving the exposedand cured photoresist in place. Known solvent application mechanisms maybe employed.

[0125] Following the wash step, the developed material (84 b) may bedried, and the completed microcup array (81) is taken up for storage orfurther processing (105).

[0126]FIG. 8A. shows in top view a portion of the mask (82). Note Line8-8 in FIG. 8A defines the cross section of the mask (82) shown in mainFIG. 8. The mask (82) comprises opaque sections (110) (generally squarein this example), which are bounded by transparent mask sections (112).

[0127]FIG. 8B shows in plan view a portion of the developed microcuparray (81). Note Line 8′-8′ in FIG. 8B defines the cross section of themicrocup array (81) shown in main FIG. 8. The exposed ITO conductor (88)in the microcup floor corresponds to the opaque mask portion (110), andthe microcup walls (84 b) correspond to the transparent mask portions(112).

[0128] The UV light shown in FIG. 8 irradiating the mask straightsection (92) may be supplied from conventional sources (not shown).Optionally, the mask drive cylinders (90, 91) may comprise a UVtransparent material, and a UV light source (not shown) may be locatedwithin either or both cylinders (90, 91) to provide additionalillumination at the edges of mask straight section (92). Optionally,additional support rollers or guides (not shown) may be included toprovide further support and alignment for mask straight section (92)and/or web straight section (103).

[0129]FIG. 8 shows a continuous coating step whereby the uncuredprecursor material (84 a) is spread upon the web (86). Known coatingmechanisms may be employed. Alternatively, the material (84 a) may beapplied in a separate operation, and pre-coated web substrate suppliedfrom storage/tensioner (104).

[0130] The photomask (82) may be synchronized in motion with the web(86) to move at the same speed using conventional drive controlmechanisms. For example, the drive cylinders (90, 91) may bemechanically coupled with drive cylinders (100, 101) (e.g., by gearingto a common drive motor) so that each rotates with the same tangentialvelocity. Alternatively, the drive cylinders may be controlled byconventional feedback circuitry to maintain coordinated motion, such asby sensors detecting the passage of ITO lines (88) on the web (86) andthe passage of corresponding opaque sections (110) on the mask (92), forexample by optical detectors (114) and (115) respectively. The detectorsignals may be used by the feedback control circuitry regulating drivespeed to maintain positive alignment of these corresponding sectionswithin the UV exposure sections (92/103). Alternative conventionalsensor systems, such as magnetic sensors, bar code scanners/markings,and the like, may be employed to provide feed back synchronizationcontrol.

[0131] The thickness of the display produced by the present processes ofthe invention as described herein can be as thin as a piece of paper,and may be flexible.

[0132] The width of the display is preferably the width of the web(typically 3-90 inches). Alternatively, the microcup array may be cut toproduce narrower displays, or one or more such microcup arrays may bemounted adjacent one another to produce wider displays.

[0133] The length of the display can be anywhere from inches tothousands of feet depending on the length of the web supply roll, sincethe roll-to-roll process can produce microcup arrays of any desiredlength.

[0134] Alternative roll-to-roll methods. In addition to employing themethod embodiment of FIG. 5, as shown in FIG. 8 (top exposure), theroll-to-roll apparatus of the invention may alternatively employ themethods of either of FIG. 6 or 7. For example, the method of FIG. 7 maybe employed, whereby the web ((86) in FIG. 8) comprises a materialtransparent to the radiation. The conductor lines ((88) in FIG. 8)correspond to the conductors (72) in FIG. 7 are opaque to the radiation,and the web is irradiated from behind section (103) by an additional UVsource (not shown).

[0135] Preparation and Sealing of Multi-Color Electrophoretic Displays.

[0136] An important aspect of this invention is a method for selectivelyfilling the micro-cups with pigment suspensions of different colors in apredetermined multicolor pattern to produce a color electrophoreticdisplay. The steps for the manufacture of a multi-color electrophoreticdisplay include:

[0137] (1) laminating or coating the formed microcup array with apositively working photoresist. Conventional photoresist compositionsand developing solutions may be used, such as novolac photoresist fromShipley (MA) or Hunt Chemical (CT), or Sumitomo (Japan). For example, alaminating composition may be used comprising a removable support suchas PET-4851 from Saint-Gobain, Worcester, Mass.; a novolac positivephotoresist such as Microposit S1818 from Shipley; and analkali-developable adhesive layer, such as a mixture of Nacor 72-8685from National Starch and Carboset 515 from BF Goodrich;

[0138] (2) selectively opening a partial set (first subset) of themicrocups by imagewise exposing the photoresist, removing the removablesupport film, and developing the positive photoresist with a developersuch as diluted Microposit 351 developer from Shipley;

[0139] (3) filling the opened cups with the electrophoretic fluid, suchas fluid containing charged white pigment (TiO₂) particles and dye orpigment of the first primary color;

[0140] (4) sealing the filled microcups as described in the preparationof monochrome displays; and

[0141] (5) repeating steps (2) through (4) for additional subsets of themicrocups, so as to create microcups filled with electrophoretic fluidof the second and the third primary colors.

[0142] FIGS. 9A-9H show a specific example of the preparation of amulti-color electrophoretic display by the method of the invention,including the following steps:

[0143]FIG. 9A: Provide a microcup array produced by one of the methodsdescribed above, the microcup array comprising a plurality of dividingwalls (120) mounted to web (121) to form an array of microcup cells(122).

[0144]FIG. 9B: Laminate the array of microcups (122) with a positivedry-film photoresist which comprises at least an adhesive layer (123),and a positive photoresist (124). Using a first photomask (not shown),imagewise expose the positive photoresist (124) by UV, visible light, orother radiation, with the exposure being limited by the mask to apredetermined first subset of the microcups of the array (122 a). Knownphotoresist compositions and laminating mechanisms may be employed.

[0145]FIG. 9C: Develop the photoresist (124) so as to open by removal ofthe photoresist (124) and adhesive layer (123) from the selected exposedmicrocup subset (122 a). Known photoresist development solvents andsolvent application mechanisms may be employed.

[0146]FIG. 9D: Fill in the opened microcup subset (122 a) with a chargedpigment dispersion (125 a) in a dielectric solvent corresponding to thefirst primary color and a thermoset sealant precursor (126 a) which isincompatible with the solvent and has a lower specific gravity than thesolvent and the pigment particles. Seal the microcups (122 a) of thefirst subset to form closed electrophoretic cells containingelectrophoretic fluid of the first primary color by curing the thermosetprecursor (126 a) (preferably by radiation such as UV, less preferablyby heat or moisture) during or after the thermoset precursor separatesand forms a supernatant layer on top of the liquid phase. The sealing ofthe microcups may be alternatively accomplished by directly coating alayer of the thermoset precursor material over the surface of the liquidphase (125 a).

[0147]FIG. 9E: Repeat the steps shown in FIG. 9B with respect to asecond selected subset (122 b) of the microcups of the array, using asecond mask to expose the second selected microcup subset (122 b).Optionally, the first mask may be moved and re-aligned so as to exposethe second subset.

[0148]FIG. 9F: Repeat the steps shown in FIG. 9C with respect to thesecond selected subset (122 b) of the microcups so as to open the secondmicrocup subset (122 b).

[0149]FIG. 9G: Repeat the steps shown in FIG. 9D with respect to thesecond selected subset (122 b) of the microcups to fill the secondmicrocup subset with a pigment/solvent dispersion (125 b) correspondingto a second primary color, and to seal the second subset (122 b) withsealant (126 b) to form closed electrophoretic cells.

[0150]FIG. 9H: Repeat the steps shown in FIGS. 9B-D with respect to thethird selected subset (122 c) of the microcups so as to expose, open,fill and seal the third subset (122 c) and form closed electrophoreticcells corresponding to a third primary color. The residual photoresist(124) and adhesive layer (123) may then be removed. The sealed array ofelectrophoretic cells is then laminated in registration to apre-patterned transparent top conductor film (127) pre-coated with anadhesive layer (128) which may be a pressure sensitive adhesive, a hotmelt adhesive, a heat, moisture, or radiation curable adhesive. Theadhesive is hardened to bond to the cells. Known laminating mechanismsand adhesives may be employed.

[0151] Synchronized Roll-to-Roll Process for Multi-Color ElectrophoreticDisplays.

[0152] An important aspect of this invention is a roll-to-roll methodfor making multi-color electrophoretic displays, whereby the process ofFIGS. 9A-H may be carried out on a continuous basis. The method includesexposing the laminated or coated microcup array through a synchronizedphotomask that is registered with the microcups and moving at the samespeed as the web carrying the laminated microcups. After exposing theselected cups, the positively working photoresist is developed andopened in the exposed areas. Color displays can then be manufactured bya semi-continuous process on a web of any desired length, which may besubdivided as desired for the final display product.

[0153]FIGS. 10, 10A and 10B show the method steps of FIGS. 9A-H carriedout by the novel synchronized roll-to-roll photo-lithographic apparatus(130) of the invention using a positive acting photoresist laminate. Thepre-formed microcup array/support web (81) is shown being fed inward atthe upper right, such as from an array storage/tensioner device (105′),which may optionally be the output (105) of the roll-to-toll arrayforming process shown in FIG. 8.

[0154] The microcup array (81) is initially laminated or coated with acontinuous strip of positive acting photoresist composition (131) whichis fed inward from photoresist storage (132). In the case of lamination,the photoresist composition (131) may comprise the adhesive layer (123)and positive photoresist (124) shown in FIG. 9. The lamination may beaccomplished by conventional laminating devices, such as by pressure oflaminating cylinders (133 a and 133 b).

[0155] The roll-to-roll photo-lithographic apparatus (130) for makingcolor displays is substantially similar to the roll-to-rollphoto-lithographic apparatus (80) for making microcup arrays shown inFIG. 8. In the preferred mounting arrangement shown in FIG. 10, the mask(136) is formed as a continuous loop, and is mounted to engage intension at least a spaced-apart pair of drive/support cylinders (140 and141), the mask loop (136) having a substantial straight section (142)spanning between the curved portions (143) which fit around the drivecylinders (140 and 141).

[0156] The microcup array (81) similarly engages and passes around atleast two spaced apart drive cylinders (150, 151), so that a straightportion (153) of the array (81) is aligned parallel to the straightsection (142) of the mask loop (136). The mask drive cylinders (140,141) are driven to rotate in the direction shown as Arrows A, and theweb drive cylinders (150, 151) are driven to rotate in the oppositedirection shown as Arrows B, so as to cause the mask straight section(142) and web straight section (153) to move in parallel, in the samedirection, at the same speed. The respective mask and web straightsections (142) and (153) respectively are preferably disposed a selectedsmall distance apart. The photomask (136) may be synchronized in motionwith the microcup array (81) by the methods described above with respectto the roll-to-roll process of FIG. 8.

[0157] Note that the orientation of the device (130) in FIG. 10 is onlyexemplary, and the elements may be re-arranged in many suitableorientations with respect to the vertical direction for carrying out themethod steps shown. Additional conventional supports, such as guides,rollers and the like, may be used to support, tension, turn, and/ortwist the microcup array (81) during the process shown.

[0158]FIG. 10A shows in plan view a portion of the mask (136). Note Line10-10 in FIG. 10A defines the cross section of the mask (136) shown inmain FIG. 10. Note that the pattern of synchronized mask (136) hastransparent sections (160) sized and aligned to permit the exposure ofthe surface (165) of a first subset of the microcups, in this example,every third microcup in linear sequence. The opaque portion of the mask(162) prevents exposure of the remaining microcups and wall area.Following UV or other radiation exposure, the photoresist (131) iswashed or treated with a suitable photoresist developer which leaves theunexposed material (131 a) in place as it removes the exposed material(131 b), so as to create an opening in the laminate of the exposedmicrocups. Following the wash step, the microcup array may be dried, andthe microcup array is taken up for storage or further processing (106).

[0159]FIG. 10B shows in plan view a portion of the microcup array (81)following delvelopment of the photoresist (131). Note Line 10′-10′ inFIG. 10B defines the cross section of the microcup array (81) shown inmain FIG. 10. The exposed ITO conductor (88) in the microcup floorcorresponds to the transparent mask portion (160), as the exposedconductor (88) of a subset of the microcups is visible through theopenings (166) formed by removal of exposed photoresist (131 b). Thebalance of the microcups and walls remain covered by unexposedphotoresist (131 a), corresponding to the transparent mask portions(162). In the example of FIG. 10, the first microcup subset, both intransparent mask sections (160) and developed photoresist openings(166), comprises staggered-offset rows, with every third microcup ineach row opened.

[0160] In FIG. 10, the microcup array (81) with the first subsetopenings (166) is shown being taken up by a second arraystorage/tensioner device (106) (not shown) as it moves outward (awayfrom the UV exposure section). Optionally, the device (106) may comprisefurther processing apparatus for continuous processing. It may be seenthat following filling and sealing the opened microcups, as describedabove with respect to FIG. 9D, the process of FIG. 10 may be repeated(on the same or additional device (130), with the transparent sections(160) of mask (136) aligned to expose and create openings in a secondmicrocup subset.

[0161]FIG. 11 illustrates schematically a semi-continuous process forthe manufacture of a 3-color EPD microcup array assembly, employing themethods described herein, particularly the methods described above inFIGS. 8, 9 and 10. The exemplary process of FIG. 11 begins with thein-feed of a pre-patterned conductor/support web from a web storagedevice (202). The web forms a continuous strip substrate upon which theprocesses of steps (204) through (238) of FIG. 11 may be performed insequence. The web may be moved, turned and guided by rollers, guideslots and the like, (not shown) as needed to bring it sequentially tothe locations of apparatus to perform these steps.

[0162] At step (204), the web/conductor is coated with radiation curableprecursor material (RCPM). At step (206), the coated web is exposed in aroll-to-roll synchronized photo-lithographic apparatus of the inventionthrough a microcup mask. At step (208), the uncured RCPM is removed bytreatment or “washing” employing suitable solvent compositions, to leavethe cured microcup array formed upon the web.

[0163] A positive acting photoresist laminate or coating is fed fromstorage device (210) and laminated or coated onto the upper surface ofthe microcup array at step (211), thereby individually enclosing themicrocups, so as to permit selective filling. The microcup array withthe photoresist is then exposed in another roll-to-roll synchronizedphoto-lithographic apparatus of the invention at step (212), using amask configured to only expose a first subset of the microcups. At step(214), the microcup array is treated or “washed” employing suitablesolvent compositions, to remove the exposed portion of the photoresist.Since Step (212) only exposed the first subset of microcups, the removalof the photoresist is only from the tops of the first subset ofmicrocups, which are thereby selectively opened. At step (216), theopened first subset of cups are filled with a first pigment/solventcomposition. At step (218), the first subset of open microcups is sealedand cured as described in FIG. 9 above. The sealing process of step(218) does not compromise the unexposed photoresist.

[0164] The microcup array is then exposed in another roll-to-rollsynchronized photo-lithographic apparatus of the invention at step (220)using a mask configured to expose a second subset of the microcups(while leaving a remaining third subset unexposed). At step (222), themicrocup array is treated or “washed” employing suitable solventcompositions, to remove the exposed portion of the photoresist. SinceStep (220) only exposed the second subset of microcups, the removal ofthe photoresist is only from the tops of this second subset, which arethereby selectively opened (leaving the third subset closed). At step(224), the opened second subset of cups are filled with a secondpigment/solvent composition. At step (226), the second subset of openmicrocups is sealed and cured as described at step (218).

[0165] The remaining photoresist is then removed at step (230), themicrocup array being treated or “washed” employing suitable solventcompositions, thereby opening the third subset of microcups. Optionally,step (230) may include exposing the remaining photoresist to radiation,to assist removal. At step (232), the opened third subset of cups arefilled with a third pigment/solvent composition. At step (234), thethird subset of open microcups is sealed and cured as described at step(218).

[0166] At step (238), a pre-patterned ITO top conductor film is fed fromITO laminated storage device (236) and is laminated to the upper surfaceof the filled and sealed microcup array. The exemplary processterminates with the out-feed of an assembled 3-color EPD microcup array(240) in the form of a continuous sealed EPD array strip. The microcuparray (240) may be out-fed to storage, or may continue to furthercontinuous sequence processing steps. In general, further processingincludes subdividing the array to form individual array portions, whichare subsequently packaged to form EPD products.

[0167] While the present invention has been described with reference tothe specific embodiments thereof, it should be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation, materials, compositions, processes, process stepor steps, to the objective, spirit and scope of the present invention.All such modifications are intended to be within the scope of the claimsappended hereto.

[0168] For example, it should be noted that the method of the inventionfor making microcups may also be used for manufacturing microcup arraysfor liquid crystal displays, as well as electrophoretic displays.Similarly, the microcup selective filling, scaling and ITO laminatingmethods of the invention may also be employed in the manufacture ofliquid crystal displays.

[0169] It is therefore wished that this invention to be defined by thescope of the appended claims as broadly as the prior art will permit,and in view of the specification if need be.

What is claimed is:
 1. A process for the preparation of a plurality ofwell-defined structures of at least one electronic device, said processincluding the imagewise exposure of radiation sensitive material, saidprocess comprises the steps of: (a) providing a support web; (b)providing a layer of radiation sensitive composition coated on saidsupport web; (c) providing a pre-patterned photomask, said photomaskcomprises a strip formed as a continuous loop, said photomask patterncorresponding in form to at least one of said structures so as to permitan image of said structure to be projected by radiation passing throughsaid photomask; (d) aligning said photomask loop adjacent to saidsupport web so that a portion of said photomask loop is in generallyparallel orientation to at least a portion of said web, (e) selectivelyimagewise exposing said radiation sensitive material by passage ofradiation through said photomask; (f) rolling said photomask loop insynchronized motion relative to said support web, said synchronizedmotion includes moving at least a portion of said photomask loop and atleast a portion of said web in parallel in substantially the samedirection.
 2. A process as in claim 1, wherein: said step of rollingsaid photomask loop includes moving at least a portion of said photomaskloop and at least a portion of said web in parallel in substantially thesame direction and at substantially the same velocity during saidexposure step.
 3. A process as in claim 2, wherein: (a) said step ofproviding an elongate support web includes that said web comprises aplurality of conductor lines for addressing microcups of at least onedisplay device; (b) said step providing a layer of radiation sensitivecomposition includes that said composition is a radiation curablematerial for said structures, said structures are a plurality ofmicrocups disposed as a microcup array for at least one display device;(c) said step of providing a pre-patterned photomask includes that saidphotomask pattern corresponding in form to said plurality of microcups,so as to permit an image of said microcups to be projected by radiationpassing through said photomask; (d) said step of selectively exposingsaid radiation sensitive material includes selectively curing a portionof said radiation curable precursor material while a portion of saidradiation curable material remains uncured, said selectively curedportion corresponding to said plurality of microcups; and (e) saidprocess includes the step of selectively removing said uncured portionof said radiation curable material while leaving on said web saidselectively cured portion, so as to form said microcup array.
 4. Aprocess as in claim 2, wherein: (a) said step of providing a support webincludes that said web comprises a plurality of pre-formed microcupsdisposed in an microcup array for at least one display device, each ofsaid microcups having a top opening; (b) said step of providing a layerof radiation sensitive composition includes that said composition is apositively working photoresist composition, and that said layer isdeposited upon said microcup array to close said plurality of microcuptop openings; (c) said step of providing a pre-patterned photomaskincludes that said photomask pattern corresponds in form to said topopenings of a first selected subset of said plurality of microcups, soas to permit an image of said top openings of said first microcup subsetto be projected by radiation passing through said photomask; (d) saidstep of selectively exposing said radiation sensitive material includesselectively exposing the portion of said photoresist layer coordinatewith said microcup top openings of said first selected microcup subset;(e) said process includes the step of selectively removing said exposedportion of said photoresist layer so as to selectively re-open the topopenings of said first selected microcup subset;
 5. A process as inclaim 4, wherein said process includes the steps of: (a) selectivelyfilling said first microcup subset via said re-opened microcup topopenings with at least one of: a first electrophoretic displaypigment/solvent composition and a first liquid crystal composition; and(b) closing and sealing said re-opened top openings of said firstmicrocup subset.
 6. A process as in claim 5, wherein: following saidstep of closing and sealing said re-opened top openings of said firstmicrocup subset, said process includes the steps of: (a) repeating saidphotomask providing step, said photomask pattern corresponds in form tosaid top openings of a second selected subset of said plurality ofmicrocups, so as to permit an image of said top openings of said secondmicrocup subset to be projected by radiation passing through saidphotomask; (b) repeating said aligning step, said selectively imagewiseexposing step, said rolling step, and said selectively removing steps,so as to selectively re-open said top openings of said second microcupsubset; (c) selectively filling said second microcup subset via saidre-opened microcup top openings with at least one of: a secondelectrophoretic display pigment/solvent composition and a second liquidcrystal composition; and (d) closing and sealing said re-opened topopenings of said second microcup subset.
 7. A process as in claim 6,wherein: following said step of closing and sealing said re-opened topopenings of said second microcup subset, said process includes the stepsof: (a) removing said photoresist layer for at least the top openings ofa third subset of microcups; (b) filling said third microcup subset viasaid re-opened microcup top openings with at least one of: a thirdelectrophoretic display pigment/solvent composition and a third liquidcrystal composition; and (c) closing and sealing said re-opened topopenings of said third microcup subset.
 8. A process as in claim 7, saidprocess includes the steps of: laminating upon said microcup array a toplaminate, said top laminate includes a plurality of pre-patternedtransparent conductor lines for addressing microcups of at least onedisplay device.
 9. A continuous process for the preparation of anassembled microcup array for at least one display device, said processcomprises the steps of: (a) carrying out the process of claim 3, so asto form said microcup array upon said support web, each of saidmicrocups having a top opening; (b) moving said web so as to permit atleast one subsequent process step to be performed on said microcup arrayin a generally continuous manner; (c) filling at least a subset of saidmicrocups via said top openings with a fluid composition including atleast one of: an electrophoretic display pigment/solvent composition anda liquid crystal display composition, and permanently closing andsealing said at least a subset of top openings of said microcups; and(d) laminating upon said microcup array a top laminate, said toplaminate includes a plurality of pre-patterned conductor lines foraddressing microcups of at least one display device, so as to form anassembled microcup array for said at least one display device.
 10. Acontinuous process as in claim 9, wherein: said step of filling, sealingand closing comprise filing substantially all of said microcups with asingle fluid composition, so as to form an assembled microcup array forat least one monochrome display device.
 11. A continuous process as inclaim 9, wherein: said steps of filling, sealing and closing comprisecarrying out the process of claim 7 to selectively fill a plurality ofmicrocup subsets with a plurality of different fluid compositions, so asto form an assembled microcup array for at least one multi-color displaydevice.
 12. A process for the preparation of a plurality of well-definedstructures of at least one electronic device, said structures beingdisposed coordinate with a plurality of elements of said at least oneelectronic device, said process including the imagewise exposure ofradiation sensitive material, said process comprises the steps of: (a)providing a support web having a surface; i. said support web includes aplurality of elements of said at least one electronic device; ii. saidelements being disposed in a repeated longitudinal pattern along saidsupport web; (b) coating a layer of radiation sensitive composition onsaid support web; (c) providing a pre-patterned photomask; i. saidphotomask comprises a strip formed as a continuous loop; ii. saidphotomask loop is configured to have a loop face adjacent to at least aportion of said web surface; iii. said photomask pattern includes aplurality of photomask portions, each of said photomask portions havingone of pre-selected transparency to radiation and pre-selected opacityto radiation corresponding in form to one of said plurality ofstructures; (d) aligning said photomask loop face in generally parallelorientation adjacent to said support web surface, including aligning ina predetermined spatial relationship at least one of said plurality ofelements to at least one of said plurality of photomask portions; (e)selectively imagewise exposing said radiation sensitive material bypassage of radiation through said photomask; (f) moving said photomaskloop face in synchronized motion relative to said support web surface,said synchronized motion includes moving said loop face and said websurface in parallel in the substantially the same direction forsubstantially the same distance so as to maintain said alignment in apredetermined spatial relationship.
 13. A process as in claim 12,wherein: said step of moving said photomask loop face in synchronizedmotion includes moving said loop face and said web surface atsubstantially the same velocity.
 14. A process as in claim 12, wherein:said step of moving said photomask loop face in synchronized motionincludes moving said loop face and said web surface at a constantrelative velocity.
 15. A process as in claim 13, wherein: said step ofmoving said photomask loop face in synchronized motion is carried outgenerally simultaneously with said step of exposing said radiationsensitive material.
 16. A process as in claim 15, wherein: said steps ofmoving said photomask loop face in synchronized motion and exposing saidradiation sensitive material are carried out generally continuously. 17.A process as in claim 16, wherein: said step of coating a layer ofradiation sensitive composition is carried out generally continuously.18. A process as in claim 15, wherein: said step of coating a layer ofradiation sensitive composition includes that said layer is one of: (a)a radiation curable precursor material for said structures; and (b) aphotoresist composition;
 19. A process as in claim 15, wherein: saidstep aligning said photomask loop includes: (a) detecting at least oneof: i. one of said elements of said web; and ii. a pre-formed marker onsaid web; (b) detecting at least one of said photomask portions; i. oneof said portions of said photomask; and ii. a pre-formed marker on saidphotomask, and; (c) controlling the motion of at least one of said weband said photomask face in response to said detections, so as to bringat least one photomask portion into a predetermined spatial relationshipwith at least one photomask portion.
 20. A process as in claim 16,wherein: (a) said step of providing said support web includes that saidplurality of elements of said at least one electronic device includes aplurality of pre-patterned conductor lines for addressing microcups ofan electronic display; (b) said step of coating a layer of radiationsensitive composition includes: i. said composition is a radiationcurable material for said structures; and ii. said structures are aplurality of microcups disposed in an array for at least one electronicdisplay iii. said microcups comprising surrounding microcup walls; (c)said step of providing a pre-patterned photomask includes each of saidplurality of photomask portions corresponds in form to at least one ofsaid walls of one of said plurality of microcups; (d) said step ofaligning in a predetermined spatial relationship includes aligning atleast one of said plurality of conductor lines coordinate with at leastone of said plurality of photomask portions corresponding to microcups;(e) said step of selectively exposing said radiation sensitive materialincludes selectively curing a portion of said radiation curableprecursor material while a portion of said radiation curable precursormaterial remains uncured, said selectively cured portion correspondingto said microcup walls.
 21. A process as in claim 20, wherein saidprocess includes the step of: following said step of selectivelyexposing said radiation sensitive material, selectively removing saiduncured portion of said radiation curable precursor material whileleaving said selectively cured portion corresponding to said microcupwalls.
 22. A process as in claim 21, wherein: said step of selectivelyremoving said uncured portion of said radiation curable precursormaterial is carried out generally continuously.
 23. A process as inclaim 16, wherein: (a) said step of providing a support web includesthat said web comprises a pre-formed array of a plurality of microcupsfor at least one electronic display, each of said microcups having a topopening; (b) said step of coating a layer of radiation sensitivecomposition includes: i. said composition is a positively workingphotoresist composition; and ii. said coating step includes depositingsaid layer upon said microcup array to close and seal said microcup topopenings; (c) said step of providing a pre-patterned photomask includesthat each of said plurality of photomask portions has a pre-selectedtransparency to radiation corresponds in form to one of a first selectedsubset of said plurality of microcups top openings; and (d) said step ofselectively exposing said radiation sensitive material includesselectively exposing the portion of said photoresist layer coordinatewith said microcup top openings of said first selected microcup subset.24. A process as in claim 23, wherein said process includes the step of:following said step of selectively exposing said photoresist layer,selectively removing said exposed portion of said photoresist layer soas to selectively re-open the top openings of said first selectedmicrocup subset.
 25. A process as in claim 24, wherein: following saidstep of selectively removing said exposed portion of said photoresist,said process includes the steps of: (a) selectively filling said firstmicrocup subset via said re-opened microcup top openings with at leastone of: i. a first electrophoretic display pigment/solvent composition;and ii. a first liquid crystal composition; (b) permanently closing andsealing said re-opened top openings of said first microcup subset.
 26. Aprocess as in claim 25, wherein: following said step of closing andsealing said re-opened top openings of said first microcup subset, saidprocess includes the steps of: (a) repeating said photomask providingstep by providing a second photomask, said second photomask includingphotomask portions corresponding in form to the top openings of a secondselected subset of said microcups; (b) repeating said aligning, moving,selectively imagewise exposing, and selectively removing steps withrespect to said second photomask and said second microcup subset, so asto selectively re-open said top openings of said second microcup subset;(c) selectively filling said second microcup subset via said re-openedmicrocup top openings with at least one of: i. a second electrophoreticdisplay pigment/solvent composition; and ii. a second liquid crystalcomposition; (d) closing and sealing said re-opened top openings of saidsecond microcup subset.
 27. A process as in claim 26, wherein: said stepof providing a web includes providing a microcup array, said arrayincludes at least a third subset of microcups distinct from said firstand second subsets; and wherein following said step of closing andsealing said re-opened top openings of said second microcup subset, saidprocess includes the steps of: (a) removing said photoresist layer forat least the top openings of said third subset of microcups; (b) fillingsaid third microcup subset via said re-opened microcup top openings withat least one of: iii. a third electrophoretic display pigment/solventcomposition; and iv. a third liquid crystal composition; (c) closing andsealing said re-opened top openings of said third microcup subset.
 28. Aprocess as in claim 27, said process includes the steps of: laminatingupon said sealed microcup array a top laminate, said top laminateincludes a plurality of pre-patterned conductor lines for addressingmicrocups of at least one display device.
 29. A process as in claim 28,said process includes the steps of: depositing a layer of adhesivebetween the said sealed microcup array and said pre-patterned conductorlines by coating or lamination.
 30. An apparatus for the preparation ofa plurality of well-defined structures of at least one electronic deviceby the imagewise exposure of a layer of radiation sensitive materialcoated upon a support web, comprising: (a) a web drive mechanismengaging said support web so as to movably guide said web; (b) apre-patterned photomask, said photomask comprises a strip formed as acontinuous loop; (c) a photomask alignment mechanism engaging saidphotomask, said alignment mechanism is mounted adjacent said web so asto align said photomask loop adjacent to said web so that a portion ofsaid photomask loop is in generally parallel orientation to at least aportion of said web; (d) a photomask drive mechanism engaging saidphotomask for rolling said photomask loop, said photomask drivemechanism is synchronizable with said web drive mechanism so as topermit rolling said photomask loop in synchronized motion relative tosaid support web, said synchronized motion includes moving at least aportion of said photomask loop and at least a portion of said web inparallel in substantially the same direction; (e) said photomask patterncorresponds in form to at least one of said structures so as to permitan image of said structure to be projected by radiation passing throughsaid photomask; and (f) a radiation source mounted in cooperativealignment with said photomask and said web so as to permit the selectiveimagewise exposure of said radiation sensitive material by passage ofradiation through said photomask.
 31. An apparatus as in claim 30,wherein: said synchronized motion of said synchronizable photomask drivemechanism includes moving at least a portion of said photomask loop andat least a portion of said web in parallel at substantially the samevelocity.
 32. An apparatus as in claim 31, wherein: (a) said support webincludes a plurality of conductor lines for addressing microcups of atleast one display device; (b) said layer of radiation sensitivecomposition is a radiation curable material for said structures, saidstructures are a plurality of microcups disposed as a microcup array forat least one display device; and (c) said photomask pattern correspondsin form to said plurality of microcups, so as to permit selectivelyexposing said precursor material by an image of said microcups projectedby radiation from said radiation source passing through said photomaskso as to selectively cure a portion of said precursor material while aportion of said precursor material remains uncured, said selectivelycured portion corresponding to said plurality of microcups.
 33. Anapparatus as in claim 32, further comprising: a solvent applicationmechanism mounted adjacent said web so as to permit the application ofat least a solvent for removing said uncured portion of said precursormaterial while leaving on said web said selectively cured portion, so asto form said microcup array upon said web.
 34. An apparatus as in claim31, wherein: (a) said support web includes a plurality of pre-formedmicrocups disposed in an microcup array for at least one display device,each of said microcups having a top opening; (b) said layer of radiationsensitive composition is a positively working photoresist compositiondeposited upon said microcup array so as to close said plurality ofmicrocup top openings; and (c) said photomask is a first photomaskhaving a first pattern; and (d) said first photomask pattern correspondsin form to said top openings of a first selected subset of saidplurality of microcups, so as to permit selectively exposing saidphotoresist layer by an image of said top openings of said firstmicrocup subset by radiation passing through said first photomask so asto expose the portion of said photoresist layer coordinate with said topopenings of said first selected microcup subset while a portion of saidphotoresist layer remains unexposed.
 35. An apparatus as in claim 34,further comprising: a solvent application mechanism mounted adjacentsaid web so as to permit application of at least a solvent for removingsaid exposed portion of said photoresist layer while leaving on saidmicrocup array said unexposed portion, so as to selectively re-open thetop openings of said first selected microcup subset.
 36. An apparatus asin claim 35, further comprising: (a) a first microcup filling mechanismmounted adjacent said web so as to permit the selective filling of saidfirst microcup subset via said re-opened microcup top openings with atleast one of: a first electrophoretic display pigment/solventcomposition and a first liquid crystal display composition; and (b) afirst microcup sealing mechanism mounted adjacent said web so as topermit the closing and sealing said re-opened top openings of said firstmicrocup subset.
 37. An apparatus as in claim 36, further comprising:(a) a second prepatterned photomask having a second pattern; (b) asecond photomask alignment mechanism engaging said second photomask,said second alignment mechanism is mounted adjacent said web so as toalign said second photomask loop adjacent to said web so that a portionof said photomask loop is in generally parallel orientation to at leasta portion of said web; (c) a second photomask drive mechanism engagingsaid second photomask for rolling said second photomask loop, saidsecond photomask drive mechanism is synchronizable with said web drivemechanism so as to permit rolling said second photomask loop insynchronized motion relative to said support web, said synchronizedmotion includes moving at least a portion of said second photomask loopand at least a portion of said web in parallel at substantially the samevelocity; and (d) a second radiation source mounted in cooperativealignment with said second photomask and said web so as to permit theselective imagewise exposure of said radiation sensitive material bypassage of radiation through said second photomask. (e) said secondphotomask pattern corresponds in form to said top openings of a secondselected subset of said plurality of microcups, so as to permitselectively exposing said photoresist layer by an image of said topopenings of said second microcup subset, and so as to expose the portionof said photoresist layer coordinate with said top openings of saidsecond selected microcup subset while a portion of said photoresistlayer remains unexposed. (f) a second solvent application mechanismmounted adjacent said web so as to permit the application of at least asolvent for removing said exposed portion of said photoresist layerwhile leaving on said microcup array said unexposed portion, so as toselectively re-open the top openings of said second selected microcupsubset; (g) a second microcup filling mechanism mounted adjacent saidweb so as to permit the selective filling of said second microcup subsetvia said re-opened microcup top openings with at least one of: a secondelectrophoretic display pigment/solvent composition and a second liquidcrystal composition; and (h) a second microcup sealing mechanism mountedadjacent said web so as to permit the closing and sealing said re-openedtop openings of said second microcup subset.
 38. An apparatus as inclaim 37, further comprising: (a) a third solvent application mechanismmounted adjacent said web so as to permit the application of at least asolvent for removing said photoresist layer on a third subset of saidplurality of microcups of said microcup array, so as to re-open the topopenings of said third microcup subset; (b) a third microcup fillingmechanism mounted adjacent said web so as to permit the filling of saidthird microcup subset via said re-opened microcup top openings with atleast one of: a third electrophoretic display pigment/solventcomposition and a third liquid crystal composition; and (c) a thirdmicrocup sealing mechanism mounted adjacent said web so as to permit theclosing and sealing said re-opened top openings of said third microcupsubset.
 39. An apparatus as in claim 38, further comprising: alaminating mechanism mounted adjacent said web so as to permit theadhesive lamination upon said microcup array of a top laminate, said toplaminate includes a plurality of pre-patterned conductor lines foraddressing microcups of at least one display device.
 40. A process as inclaim 2, wherein the conductor lines are transparent to visible light.41. A process as in claim 8, wherein the conductor lines are transparentto visible light.
 42. A process as in claim 20, wherein the conductorlines are transparent to visible light.
 43. A process as in claim 28,wherein the conductor lines are transparent to visible light.
 44. Aprocess as in claim 32, wherein the conductor lines are transparent tovisible light.
 45. A process as in claim 39, wherein the conductor linesare transparent to visible light.